Micropropagation of apple--a review

Application of Biotechniques for In Vitro Virus and Viroid Elimination in Pome Fruit Crops

Sustainable production of pome fruit crops is dependent upon having virus-free planting materials. The production and distribution of plants derived from virus- and viroid-negative sources is necessary not only to control pome fruit viral diseases but also for sustainable breeding activities, as well as the safe movement of plant materials across borders. With variable success rates, different in vitro-based techniques, including shoot tip culture, micrografting, thermotherapy, chemotherapy, and shoot tip cryotherapy, have been employed to eliminate viruses from pome fruits. Higher pathogen eradication efficiencies have been achieved by combining two or more of these techniques. An accurate diagnosis that confirms complete viral elimination is crucial for developing effective management strategies. In recent years, considerable efforts have resulted in new reliable and efficient virus detection methods. This comprehensive review documents the development and recent advances in biotechnological methods that produce healthy pome fruit plants. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

In Vitro Collection for the Safe Storage of Grapevine Hybrids and Identification of the Presence of Plasmopara viticola Resistance Genes

This paper focuses on the creation of an in vitro collection of grapevine hybrids from the breeding program of the Kazakh Scientific Research Institute of Fruit Growing and Viticulture and investigates the presence of Plasmopara viticola resistance mediated by Rpv3 and Rpv12 loci. We looked at the optimization of in vitro establishment using either shoots taken directly from field-grown plants or from budwood cuttings forced indoors. We further screened for the presence of endophyte contamination in the initiated explants and optimized the multiplication stage. Finally, the presence of the resistance loci against P. viticola was studied. The shoots initiated from the field-sourced explants were the more effective method of providing plant sources for in vitro initiation once all plant accessions met the goal of in vitro establishment. The concentration of phytohormones and the acidity of the culture medium have a great effect on the multiplication rate and the quality of in vitro stock cultures. Out of 17 grapevine accessions, 16 showed the presence of single or combined resistance loci against P. viticola. The grapevine accessions identified as carrying Rpv3 and Rpv12 alleles represent important genetic resources for disease resistance breeding programs. These accessions may further contribute to the creation of new elite cultivars of economic interest.

Assessment of genetic homogeneity of in-vitro propagated apple root stock MM 104 using ISSR and SCoT primers

Apple is an important fruit crop that is always in demand due to its commercial and nutraceutical value. Also, the requirement for quality planting material for this fruit crop for new plantations is increasing continuously. In-vitro propagation is an alternative approach, which may help to produce genetically identical high grade planting material. In this study, for the first time, an efficient and reproducible propagation protocol has been established for apple root stock MM 104 via axillary bud. Culturing axillary buds on Murashige and Skoog apple rootstock (MM 104) resulted in better in-vitro propagation. (MS) basal medium supplemented with 3.0% (w/v) sucrose and 0.8% (w/v) agar. The axillary buds were established in MS basal medium with BA (5.0 µM), NAA (1.0 µM) and further used to establish invitro propagation protocol. Plant Growth Regulators (PGRs), BA (1.0 µM) in combination with NAA (1.0 µM) was found most efficient for shoot multiplication (100%) and produced 9.8 shoots/explants with an average shoot length of (2.4 ± cm). All the shoots produced roots in 0.1 µM IBA with a 5-day dark period. Acclimatization of in-vitro raised plantlets was obtained with vermiculite: perlite: sand: soil (2:2:1:1) resulting in 76% survival under field conditions. The study showed that the use of axillary bud is efficient for multiple-shoot production of apple rootstock (MM 104). This is the first comprehensive report on in-vitro growth of apple root stock MM 104 with an assessment of genetic stability using DNA fingerprinting profiles based on Inter Simple Sequence Repeats (ISSR) and Start Codon Targeted (SCoT). The genetic stability of in-vitro-produced plants, as determined by SCoT and ISSR primers, demonstrated genetic closeness to the mother plant.

Effect of Plant Preservative MixtureTM on Endophytic Bacteria Eradication from In Vitro-Grown Apple Shoots

Endophytic contaminants are a common problem for the in vitro propagation of woody plants and have significant economic repercussions for the conservation of plant genetic resources and commercial micropropagation. In this study, first, the microbial contamination that appeared around the base of in vitro-grown apple shoots was identified as Bacillus megaterium. Then, plant preservative mixture (PPM^TM) was used as a bactericidal agent in plant tissue culture. Its efficacy for eradicating endophytic B. megaterium in in vitro cultures of apple was tested. In vitro-contaminated shoots were grown in tissue culture medium supplemented with 0.2% v/v PPM^TM for 12 weeks and then transferred to medium without any PPM^TM and cultured for 24 weeks. This study showed that PPM^TM is an effective agent for controlling the growth of B. megaterium. Our results highlight the species-specific response of apple shoots to PPM^TM. PPM^TM was effective in controlling endogenous microbial contaminations from apple varieties 'Golden Delicious', 'Landsberger Renette', 'Suislepper', and 'Aport krovavo-krasnyi'; meanwhile, in 'KG 7' and 'Gold Rush', all the plants grown in the absence of PPM^TM were still bacterially contaminated, even though they were pre-treated for 12 weeks in PPM^TM-supplemented medium. These results therefore suggest the essentiality of further testing of extended incubation of PPM^TM in these cultivars that had outbreaks of bacterial contamination.

Using plant growth-promoting microorganisms (PGPMs) to improve plant development under in vitro culture conditions

The use of beneficial microorganisms improves the performance of in vitro - cultured plants through the improvement of plant nutrition, the biological control of microbial pathogens or the production of phytohormones that promote plant growth and development. Plant in vitro culture techniques are highly useful to obtain significant amounts of true-to-type and disease-free plant materials. One of these techniques is clonal micropropagation which consists on the establishment of shoot tip cultures, shoot multiplication, in vitro rooting and acclimatization to ex vitro conditions. However, in some cases, the existence of recalcitrant genotypes, with a compromised multiplication and rooting ability, or the difficulties to overcome the overgrowth of endophytic contaminations might seriously limit its efficiency. In this sense, the establishment of beneficial interactions between plants and plant growth-promoting microorganisms (PGPMs) under in vitro culture conditions might represent a valuable approach to efficiently solve those restrictions. During the last years, significant evidence reporting the use of beneficial microorganisms to improve the yield of in vitro multiplication or rooting as well as their acclimatization to greenhouse or soil conditions have been provided. Most of these positive effects are strongly linked to the ability of these microorganisms to provide in vitro plants with nutrients such as nitrogen or phosphorous, to produce plant growth regulators, to control the growth of pathogens or to mitigate stress conditions. The culture of A. thaliana under aseptic conditions has provided high-quality knowledge on the root development signaling pathways, involving hormones, triggered in the presence of PGPMs. Overall, the present article offers a brief overview of the use of microorganisms to improve in vitro plant performance during the in vitro micropropagation stages, as well as the main mechanisms of plant growth promotion associated with these microorganisms.

Effects of Biogenic ZnO Nanoparticles on Growth, Physiological, Biochemical Traits and Antioxidants on Olive Tree In Vitro

Currently, there is an increasing interest in nanotechnology, since some nanomaterials can enhance crop growth, yield, nutritional status, and antioxidant defences. This work aimed to investigate for the first time the influence of zinc oxide nanoparticles (ZnO-NPs) on the in vitro growth and biochemical parameters of the olive tree (cv. Moraiolo). With this goal, biogenic ZnO-NPs (spherical shape and dimensions in the range of 10–20 nm), deriving from a green synthesis carried out with a Lemna minor L. extract were used. Different concentrations (0, 2, 6 and 18 mg L−1) of ZnO-NPs were added to the olive growth medium (OM substrate), and three sub-cultures of 45 days each were carried out. ZnO-NPs at 6 and 18 mg L−1 enhanced some growth parameters in the olive tree explants, such as the number of shoots, green fresh and total dry weight. Moreover, the abovementioned concentrations raised the chlorophyll a and b content and soluble protein. Finally, concerning the dosage applied, the treatments stimulated the content of carotenoids, anthocyanins, total phenol content (TPC), and the radical scavenging activity towards DPPH (2.2-diphenyl-1-picrylhydrazyl). In conclusion, this study highlighted that biogenic ZnO-NPs exerted beneficial effects on the olive tree explants in vitro, improving the effectiveness of the micropropagation technique.

Biotechnological Advances in Pharmacognosy and In Vitro Manipulation of Pterocarpus marsupium Roxb

Trees are vital resources for economic, environmental, and industrial growth, supporting human life directly or indirectly through a wide variety of therapeutic compounds, commodities, and ecological services. Pterocarpus marsupium Roxb. (Fabaceae) is one of the most valuable multipurpose forest trees in India and Sri Lanka, as it is cultivated for quality wood as well as pharmaceutically bioactive compounds, especially from the stem bark and heartwood. However, propagation of the tree in natural conditions is difficult due to the low percentage of seed germination coupled with overexploitation of this species for its excellent multipurpose properties. This overexploitation has ultimately led to the inclusion of P. marsupium on the list of endangered plant species. However, recent developments in plant biotechnology may offer a solution to the overuse of such valuable species if such advances are accompanied by technology transfer in the developing world. Specifically, techniques in micropropagation, genetic manipulation, DNA barcoding, drug extraction, delivery, and targeting as well as standardization, are of substantial concern. To date, there are no comprehensive and detailed reviews of P. marsupium in terms of biotechnological research developments, specifically pharmacognosy, pharmacology, tissue culture, authentication of genuine species, and basic gene transfer studies. Thus, the present review attempts to present a comprehensive overview of the biotechnological studies centered on this species and some of the recent novel approaches for its genetic improvement.

High-Frequency Plant Regeneration, Genetic Uniformity, and Flow Cytometric Analysis of Regenerants in Rutachalepensis L

Ruta chalepensis L., an evergreen shrub in the citrus family, is well-known around the world for its essential oils and variety of bioactivities, indicating its potential medicinal applications. In this study, we investigated the effect of different culture conditions, including plant growth regulators, media types, pH of the medium, and carbon sources, on in vitro regeneration from nodal explants of R. chalepensis. Following 8 weeks of culture, the highest percentage of regeneration (96.3%) and maximum number of shoots (40.3 shoot/explant) with a length of 4.8 cm were obtained with Murashige and Skoog (MS) medium at pH 5.8, supplemented with 3.0% sucrose and 5.0 µM 6-Benzyladenine (BA) in combination with 1.0 µM 1-naphthaleneacetic acid (NAA). For rooting, individually harvested shootlets were transferred on ½ MS (half-strength) supplemented with IAA (indole-3-acetic acid), IBA (indole 3-butyric acid), or NAA, and the best response in terms of root induction (91.6%), number of roots (5.3), and root mean length (4.9 cm) was achieved with 0.5 µM IBA after 6 weeks. An average of 95.2 percent of healthy, in vitro regenerated plantlets survived after being transplanted into potting soil, indicating that they were effectively hardened. DNA assays (PCR-based markers) such as random amplification of polymorphic DNA (RAPD) and directed amplification of minisatellite-region (DAMD) were employed to assess in vitro cultivated R. chalepensis plantlets that produced a monomorphic banding pattern confirming the genetic stability. Additionally, no changes in the flow cytometric profile of ploidy between regenerated plantlets and donor plants were detected. Regeneration of this valuable medicinal plant in vitro will open up new avenues in pharmaceutical biotechnology by providing an unconventional steadfast system for mass multiplication and might be effectively used in genetic manipulation for enhanced bioactive constituents.

The First Evidence of the Beneficial Effects of Se-Supplementation on In Vitro Cultivated Olive Tree Explants

Selenium is an essential micronutrient that provides important benefits to plants and humans. At proper concentrations, selenium increases plant growth, pollen vitality, the shelf life of fresh products, and seems to improve stress resistance; these effects can certainly be attributed to its direct and indirect antioxidant capacity. For these reasons, in the present work, the effects of selenium at different dosages on in vitro cultivated olive explants were investigated to observe possible positive effects (in terms of growth and vigor) on the proliferation phase. The work was carried out on four different olive cultivars: "San Felice", "Canino", "Frantoio", and "Moraiolo". The explants were cultured in aseptic conditions on olive medium (OM), with the addition of 4 mg·L^-1 of zeatin, 30 g·L^-1 of sucrose, and 7 g·L^-1 of agar. The experimental scheme included a comparison between explants grown with five different concentrations of Na₂SeO₄ (0, 10, 20, 40, and 80 mg L^-1) added to the medium during three successive subcultures. Interesting information has emerged from the results and all varieties responded to different concentrations of Selenium. The optimal Se dosages varied for each cultivar, but in general, Se concentration between 10 and 40 mg L^-1 increased fresh and dry weight of the explants and shoot lengths. Se treatment induced in all cultivars and for all dosages used an increase in total Se content in proliferated explants. Furthermore, as the subcultures proceeded, the ability of the explants to absorb Se did not diminish. The Se content ranged from 8.55 to 114.21 µg kg^-1 plant DW in 'Frantoio', from 9.83 to 94.85 µg kg^-1 plant DW in 'Moraiolo', from 19.84 to 114.21 µg kg^-1 plant DW in 'Canino', and from 20.97 to 95.54 µg kg^-1 plant DW in 'San Felice'. In general, the effect of selenium tends to decrease with the progress of subcultures and this suggests a sort of "adaptation" effect of the explants to its presence. The present study highlights for the first time the possibility of using in vitro cultures as biotechnological support to study supplementation with selenium and its effects on in vitro olive plant growth.

Application of CRISPR/Cas9 technology in wild apple (Malus sieverii) for paired sites gene editing

BACKGROUND

Xinjiang wild apple is an important tree of the Tianshan Mountains, and in recent years, it has undergone destruction by many biotic and abiotic stress and human activities. It is necessary to use new technologies to research its genomic function and molecular improvement. The clustered regulatory interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) system has been successfully applied to genetic improvement in many crops, but its editing capability varies depending on the different combinations of the synthetic guide RNA (sgRNA) and Cas9 protein expression devices.

RESULTS

In this study, we used 2 systems of vectors with paired sgRNAs targeting to MsPDS. As expected, we successfully induced the albino phenotype of calli and buds in both systems.

CONCLUSIONS

We conclude that CRISPR/Cas9 is a powerful system for editing the wild apple genome and expands the range of plants available for gene editing.

In vitro plant regeneration system for date palm (Phoenix dactylifera L.): effect of chelated iron sources

Background

Iron chelate sources and their concentrations are important factors in in vitro propagation of date palm. This study’s objective was to investigate the effect of the iron chelated form on the growth and development of tissue cultures of Barhee cultivar.

Results

The addition of FeEDDHA to the culture medium was more effective than FeEDTA on callus growth, shoot regeneration, and the number of shoots per jar, where the best result (220.8mg callus, 86.67% and 17.2 shoots per jar, respectively) was obtained by using 93.5 mg L⁻¹ FeEDDHA (5.6 mg L⁻¹ Fe), compared with other treatments. The results also indicate that using 93.5 mg L⁻¹ FeEDDHA (5.6 mg L⁻¹ Fe) as a supplement can decrease antioxidant enzymes CAT and POD activity compared to the rest of the treatments. Medium equipped with 187.0 mg L⁻¹ FeEDDHA (11.2 mg L⁻¹Fe) had the highest rooting percentage and number of roots per shoot than other treatments. The biochemical analysis results showed that treatments with FeEDDHA of 280.5 mg L⁻¹ (16.8 mg L⁻¹ Fe) and 187.0 mg L⁻¹ (11.2 mg L⁻¹Fe) significantly increased the iron content. The results showed that shoot maximum chlorophyll and endogenous IAA level content were recorded in a medium supplemented with 187.0 mg L⁻¹ FeEDDHA (11.2 mg L⁻¹Fe) as Fe source.

Conclusion

FeEDDHA used in the present study was proven to be a promising iron chelate source in comparison with the FeEDTA sources.

Phytotoxicity and Other Adverse Effects on the In Vitro Shoot Cultures Caused by Virus Elimination Treatments: Reasons and Solutions

In general, in vitro virus elimination is based on the culture of isolated meristem, and in addition thermotherapy, chemotherapy, electrotherapy, and cryotherapy can also be applied. During these processes, plantlets suffer several stresses, which can result in low rate of survival, inhibited growth, incomplete development, or abnormal morphology. Even though the in vitro cultures survive the treatment, further development can be inhibited; thus, regeneration capacity of treated in vitro shoots or explants play also an important role in successful virus elimination. Sensitivity of genotypes to treatments is very different, and the rate of destruction largely depends on the physiological condition of plants as well. Exposure time of treatments affects the rate of damage in almost every therapy. Other factors such as temperature, illumination (thermotherapy), type and concentration of applied chemicals (chemo- and cryotherapy), and electric current intensity (electrotherapy) also may have a great impact on the rate of damage. However, there are several ways to decrease the harmful effect of treatments. This review summarizes the harmful effects of virus elimination treatments applied on tissue cultures reported in the literature. The aim of this review is to expound the solutions that can be used to mitigate phytotoxic and other adverse effects in practice.

Rhizosphere microorganisms enhance in vitro root and plantlet development of Pyrus and Prunus rootstocks

The in vitro application of rhizosphere microorganisms led to a higher rooting percentage in Pyrus Py12 rootstocks and increased plant growth of Pyrus Py170 and Prunus RP-20. The rooting of fruit tree rootstocks is the most challenging step of the in vitro propagation process. The use of rhizosphere microorganisms to promote in vitro rooting and plant growth as an alternative to the addition of chemical hormones to culture media is proposed in the present study. Explants from two Pyrus (Py170 and Py12) rootstocks and the Prunus RP-20 rootstock were inoculated with Pseudomonas oryzihabitans PGP01, Cladosporium ramotenellum PGP02 and Phoma sp. PGP03 following two different methods to determine their effects on in vitro rooting and plantlet growth. The effects of the microorganisms on the growth of fully developed Py170 and RP-20 plantlets were also studied in vitro. All experiments were conducted using vermiculite to simulate a soil system in vitro. When applied to Py12 shoots, which is a hard-to-root plant material, both C. ramotenellum PGP02 and Phoma sp. PGP03 fungi were able to increase the rooting percentage from 56.25% to 100% following auxin indole-3-butyric acid (IBA) treatment. Thus, the presence of these microorganisms clearly improved root development, inducing a higher number of roots and causing shorter roots. Better overall growth and improved stem growth of treated plants was observed when auxin treatment was replaced by co-culture with microorganisms. A root growth-promoting effect was observed on RP-20 plantlets after inoculation with C. ramotenellum PGP02, while P. oryzihabitans PGP01 increased root numbers for both Py170 and RP-20 and increased root growth over stem growth for RP-20. It was also shown that the three microorganisms P. oryzihabitans PGP01, C. ramotenellum PGP02 and Phoma sp. PGP03 were able to naturally produce auxin, including indole-3-acetic acid (IAA), at different levels. Overall, our results demonstrate that the microorganisms P. oryzihabitans PGP01 and C. ramotenellum PGP02 had beneficial effects on in vitro rooting and plantlet growth and could be applied to in vitro tissue culture as a substitute for IBA.

Influence of different concentrations of 6-benzylaminopurine and thidiazuron on the proliferative activity of apple varieties in in vitro culture

An essential role in the process of clonal micropropagation is played by cytokinins, with the help of which apical dominance is removed and the formation of additional shoots and buds is activated. The article presents the study results of microshoots’ proliferative activity of apple varieties on media with 6-benzylaminopurine at a concentration of 1.0 mg/l, 2.0 mg/l and thidiazuron at a concentration of 0.1 mg/l, 0.2 mg/l and 0.3 mg/l. The objects of research were apple varieties of the VNIISPK selection - Bolotovskoe, Imrus, Veteran, Kandil orlovsky, Girlyanda, Priokskoe. The aim of the research was to study the effect of substances with cytokinin activity on the morphogenesis of apple varieties. As a result of the research, it was revealed that both cytokinins and varietal characteristics influence the multiplication factor. The highest multiplication factor was observed when using 6-BAP. Thidiazuron reduced the proliferation rate. When using 6-BAP, Bolotovskoe, Girlyanda and Priokskoe varieties had the highest multiplication factor among the varieties. When using TDZ - varieties Bolotovskoe and Kandil Orlovsky.

Influence of climatic conditions of the introduction period and varietal characteristics of black currant (Ribes nigrum L.) on the effectiveness of culture initiation in vitro

The article presents data from the effectiveness studies of the initial introduction stage of black currant (Ribes nigrum L.) into in vitro culture depending on the introduction period and the corresponding climatic conditions. The research objects were varieties of black currants selected by the Russian Research Institute of Fruit Crop Breeding: Azhurnaya, Orlovskaya serenada, Ocharovanie, Chudnoye mgnovenye. The introduction into in vitro culture was carried out in several periods characterized by different physiological states of the explants: the period of dormancy release (mid-March), the period of active growth (June), and the period of growth decay (mid-September). The source material in the spring and autumn periods were the buds of one-year stiffened shoots, in the summer introduction period - the buds of growing green shoots. The cultivation was carried out on Murashige-Skoog medium supplemented with 6-BAP (0.5 mg/l). It was noted that the survival rate of explants is determined by the physiological state of the source material due to the corresponding agro-climatic conditions during the introduction period, as well as the genotypic characteristics of the varieties. Thus, explants isolated during the active growing season are characterized by a higher and more stable survival rate. When explants were cultivated in spring and autumn, the physiological state of the explants and their survival rate were influenced by the genotypic response of varieties to the corresponding agroclimatic conditions.

Genome-Wide Characterization of the HSP20 Gene Family Identifies Potential Members Involved in Temperature Stress Response in Apple

Apple (Malus domestica Borkh.), an economically important tree fruit worldwide, frequently suffers from temperature stress during growth and development, which strongly affects the yield and quality. Heat shock protein 20 (HSP20) genes play crucial roles in protecting plants against abiotic stresses. However, they have not been systematically investigated in apple. In this study, we identified 41 HSP20 genes in the apple 'Golden Delicious' genome. These genes were unequally distributed on 15 different chromosomes and were classified into 10 subfamilies based on phylogenetic analysis and predicted subcellular localization. Chromosome mapping and synteny analysis indicated that three pairs of apple HSP20 genes were tandemly duplicated. Sequence analysis revealed that all apple HSP20 proteins reflected high structure conservation and most apple HSP20 genes (92.6%) possessed no introns, or only one intron. Numerous apple HSP20 gene promoter sequences contained stress and hormone response cis-elements. Transcriptome analysis revealed that 35 of 41 apple HSP20 genes were nearly unchanged or downregulated under normal temperature and cold stress, whereas these genes exhibited high-expression levels under heat stress. Subsequent qRT-PCR results showed that 12 of 29 selected apple HSP20 genes were extremely up-regulated (more than 1,000-fold) after 4 h of heat stress. However, the heat-upregulated genes were barely expressed or downregulated in response to cold stress, which indicated their potential function in mediating the response of apple to heat stress. Taken together, these findings lay the foundation to functionally characterize HSP20 genes to unravel their exact role in heat defense response in apple.

Genome-Wide Characterization of the HSP20 Gene Family Identifies Potential Members Involved in Temperature Stress Response in Apple

Apple (Malus domestica Borkh.), an economically important tree fruit worldwide, frequently suffers from temperature stress during growth and development, which strongly affects the yield and quality. Heat shock protein 20 (HSP20) genes play crucial roles in protecting plants against abiotic stresses. However, they have not been systematically investigated in apple. In this study, we identified 41 HSP20 genes in the apple ‘Golden Delicious’ genome. These genes were unequally distributed on 15 different chromosomes and were classified into 10 subfamilies based on phylogenetic analysis and predicted subcellular localization. Chromosome mapping and synteny analysis indicated that three pairs of apple HSP20 genes were tandemly duplicated. Sequence analysis revealed that all apple HSP20 proteins reflected high structure conservation and most apple HSP20 genes (92.6%) possessed no introns, or only one intron. Numerous apple HSP20 gene promoter sequences contained stress and hormone response cis-elements. Transcriptome analysis revealed that 35 of 41 apple HSP20 genes were nearly unchanged or downregulated under normal temperature and cold stress, whereas these genes exhibited high-expression levels under heat stress. Subsequent qRT-PCR results showed that 12 of 29 selected apple HSP20 genes were extremely up-regulated (more than 1,000-fold) after 4 h of heat stress. However, the heat-upregulated genes were barely expressed or downregulated in response to cold stress, which indicated their potential function in mediating the response of apple to heat stress. Taken together, these findings lay the foundation to functionally characterize HSP20 genes to unravel their exact role in heat defense response in apple.

Shoot tip necrosis of in vitro plant cultures: a reappraisal of possible causes and solutions

Shoot tip necrosis is a physiological condition that negatively impacts the growth and development of in vitro plant shoot cultures across a wide range of species. Shoot tip necrosis is a physiological condition and disorder that can arise in plantlets or shoots in vitro that results in death of the shoot tip. This condition, which can spread basipetally and affect the emergence of axillary shoots from buds lower down the stem, is due to the cessation of apical dominance. STN can occur at both shoot multiplication and rooting stages. One of the most common factors that cause STN is nutrient deficiency or imbalance. Moreover, the presence or absence of plant growth regulators (auxins or cytokinins) at specific developmental stages may impact STN. The cytokinin to auxin ratio within an in vitro plant can be modified by varying the concentration of cytokinins used in the culture medium. The supply of nutrients to in vitro shoots or plantlets might also affect their hormonal balance, thus modifying the occurrence of STN. High relative humidity within culture vessels and hyperhydricity are associated with STN. An adequate supply of calcium as the divalent cation (Ca²⁺) can hinder STN by inhibiting the accumulation of phenolic compounds and thus programmed cell death. Moreover, the level of Ca²⁺ affects auxin transport and ethylene production, and higher ethylene production, which can occur as a result of high relative humidity in or poor ventilation of the in vitro culture vessel, induces STN. High relative humidity can decrease the mobility of Ca²⁺ within a plant, resulting in Ca²⁺ deficiency and STN. STN of in vitro shoots or plantlets can be halted or reversed by altering the basal medium, mainly the concentration of Ca²⁺, adjusting the levels of auxins or cytokinins, or modifying culture conditions. This review examines the literature related to STN, seeks to discover the associated factors and relations between them, proposes practical solutions, and attempts to better understand the mechanism(s) underlying this condition in vitro.

Applications of Cytokinins in Horticultural Fruit Crops: Trends and Future Prospects

Cytokinins (CKs) are a chemically diverse class of plant growth regulators, exhibiting wide-ranging actions on plant growth and development, hence their exploitation in agriculture for crop improvement and management. Their coordinated regulatory effects and cross-talk interactions with other phytohormones and signaling networks are highly sophisticated, eliciting and controlling varied biological processes at the cellular to organismal levels. In this review, we briefly introduce the mode of action and general molecular biological effects of naturally occurring CKs before highlighting the great variability in the response of fruit crops to CK-based innovations. We present a comprehensive compilation of research linked to the application of CKs in non-model crop species in different phases of fruit production and management. By doing so, it is clear that the effects of CKs on fruit set, development, maturation, and ripening are not necessarily generic, even for cultivars within the same species, illustrating the magnitude of yet unknown intricate biochemical and genetic mechanisms regulating these processes in different fruit crops. Current approaches using genomic-to-metabolomic analysis are providing new insights into the in planta mechanisms of CKs, pinpointing the underlying CK-derived actions that may serve as potential targets for improving crop-specific traits and the development of new solutions for the preharvest and postharvest management of fruit crops. Where information is available, CK molecular biology is discussed in the context of its present and future implications in the applications of CKs to fruits of horticultural significance.

Stable and efficient transformation of apple

Apple is one of precious fruit crop grown in temperate zone. In the post genomic era, the analysis of gene functions in horticultural crops such as apple is required for agricultural utilization. For analysis of such crops, the protocol establishment of tissue culture and transformation is essential. Although transformation efficiency in family Rosaceae is generally very low, some cultivars of Malus species have high transformation ability. Apple cultivars are usually clonally propagated by grafting on rootstocks, which can affect fruit quality and maturity and scion productivity. Apple rootstock cultivar Japan Morioka 2 (JM2) was produced at the Division of Apple Research, Institute of Fruit and Tea Science, NARO, in Japan. JM2, which was developed for dwarfing scions and improving disease resistance, is easily propagated by hardwood cutting. Furthermore, JM2 can be stably transformed at a high efficiency, which is better than other JM series rootstocks derived from the same parent. Leaflets of cultured shoots of JM2 have been transformed using Agrobacterium (Rhizobium) with a transducing gene. In this article, the JM2 transformation protocol is introduced in detail. Various genes and promoters have been confirmed to function as expected, with the resultant transformants exhibiting specific staining and fluorescent signals, and modified floral organ shapes, precious blooming and other characteristics. JM2 is thus a useful rootstock material for the enhancement of genetic research on apple and its relatives.

Somatic Embryogenesis and Plantlet Regeneration in the Carica papaya L. cv. Eksotika

A highly efficient protocol for regeneration of Carica papaya L. cv. Eksotika somatic embryos from immature zygotic embryos was developed. This study was designed to overcome the obstacles in regeneration of somatic embryos from immature zygotic embryos of “Eksotika”, especially problems associated with formation of better root quality and callus formation at the base of somatic embryos. Somatic embryos were generated by incubation of immature zygotic embryos in half-strength salt Murashige and Skoog (MS) medium with full-strength vitamins supplemented with 7.5 mg L⁻¹ 2,4-D, 100 mg L⁻¹ L-glutamine, 50 mg L⁻¹myo-inositol, 45 mg L⁻¹ adenine sulphate, 0.33% gelrite, and 6% sucrose, followed by transfer to maturation medium consisting of ½ MS medium supplemented with 5 mg L⁻¹ phloroglucinol, 100 mg L⁻¹ L-glutamine, 100 mg L⁻¹myo-inositol, 68 mg L⁻¹ adenine sulphate, 0.38% gelrite, and 3% sucrose. After that, well-formed somatic embryos were transferred to MS medium containing 3% sucrose and 0.8% agar for shoot production. The embryos were elongated in MS medium supplemented with 1 mg L⁻¹ gibberellic acid, 0.5 mg L⁻¹ indole-3-butyric acid, 100 mg L⁻¹myo-inositol, and 3.76 mg L⁻¹ riboflavin. Root regeneration was achieved on MS medium containing 7.9 mg L⁻¹ phloroglucinol and supported with vermiculite after 4 days of cultivation on ½ MS medium with 2 mg L⁻¹ indole-3-butyric acid. After the rooting phase, in vitro plantlets were acclimatized in peat moss soil.

In Vitro Regeneration Potential of White Lupin (Lupinus albus) from Cotyledonary Nodes

The tissue culture regeneration system of Lupinus albus has always been considered as recalcitrant material due to its genotype-dependent response and low regeneration efficiency that hamper the use of genetic engineering. Establishment of repeatable plant regeneration protocol is a prerequisite tool for successful application of genetic engineering. This aim of this study was to develop standardized, efficient protocol for successful shoot induction from cotyledonary node of white lupin. In this study, 5 day old aseptically cultured seedlings were used to prepare three explants (half cotyledonary node, HCN; whole cotyledonary node, WCN; and traditional cotyledonary node, TCN), cultured on four concentrations of M519 medium (M519, ½ M519, 1/3 M519, and ¼ M519), containing four carbohydrate sources (sucrose, fructose, maltose, and glucose), and stimulated with various combinations of KT (kinetin), and NAA (naphthalene acetic acid) for direct shoot regeneration. High frequency of 80% shoot regeneration was obtained on ½ M519 medium (KT 4.0 mg L-1 + NAA 0.1 mg L-1) by using HCN as an explant. Interestingly, combinations of (KT 4.0 mg L-1 + NAA 0.1 mg L-1 + BAP 1.67 mg L-1), and (KT 2.0 mg L-1 + NAA 0.1 mg L-1) showed similar shoot regeneration frequency of 60%. Augmentation of 0.25 g L-1 activated charcoal (AC) not only reduced browning effect but also improved shoot elongation. Among the all carbohydrate sources, sucrose showed the highest regeneration frequency with HCN. Additionally, 80% rooting frequency was recorded on ½ M519 containing IAA 1.0 mg L-1 + KT 0.1 mg L-1 (indole acetic acid) after 28 days of culturing. The present study describes establishment of an efficient and successful protocol for direct plant regeneration of white lupin from different cotyledonary nodes.

An efficient in vitro regeneration system from different wild apple (Malus sieversii) explants

BACKGROUND

Wild apple, Malus sieversii, is an endangered species and a valuable genetic resource that requires a variety of conservation techniques. This study aimed to investigate the influence of different concentrations of hormones on wild apple regeneration from leaf and stem explants to establish an optimal regeneration system.

RESULTS

Leaves and stems derived from seedlings were cultured on several media supplemented with various concentrations of thidiazuron (TDZ) or 6-benzylaminopurine (BA) in different combinations with 1-naphthaleneacetic acid (NAA). The results showed that the most efficient shoot formation media (35% and 90%) were MS medium containing 4.0 mg L^-1 TDZ and 1.0 mg L^-1 NAA for leaf explants and MS medium containing 1.0 mg L^-1 BA without NAA for stem explant. MS medium supplemented with 0.4 mg L^-1 BA and 0.1 mg L^-1 NAA (for shoot multiplication) and 1/2 MS + 0.1 mg L^-1 NAA + 1.5% sucrose (for rooting) were effective media. Shoot regeneration from leaf explants was the most effective when the explants were placed abaxial side down onto the medium and were subjected to a pre-treatment of 3 weeks in darkness.

CONCLUSIONS

An optimized regeneration system for M. sieversii that allowed regeneration within 2-3 months developed. The protocol developed herein can be used in large-scale clonal propagation for the conservation of wild apple, M. sieversii.

In vitro tissue culture of apple and other Malus species: recent advances and applications

Studies on the tissue culture of apple have allowed for molecular, biotechnological and applied breeding research to advance. In the past 8 years, over 100 papers advancing basic biology, genetic transformation and cryobiology have emerged. Apple (Malus × domestica Borkh.; Rosaceae) is an important fruit crop grown mainly in temperate regions of the world. In vitro tissue culture is a biotechnological technique that has been used to genetically improve cultivars (scions) and rootstocks. This updated review presents a synthesis of findings related to the tissue culture of apple and other Malus spp. between 2010 and 2018. Increasingly complex molecular studies that are examining the apple genome, for example, in a bid to identify the cause of epigenetic mutations and the role of transposable elements in this process would benefit from genetically stable source material, which can be produced in vitro. Several notable or curious in vitro culture methods have been reported to improve shoot regeneration and induce the production of tetraploids in apple cultivars and rootstocks. Existing studies have revealed the molecular mechanism underlying the inhibition of adventitious roots by cytokinin. The use of the plant growth correction factor allows hypothetical shoot production from leaf-derived thin cell layers relative to conventional leaf explants to be determined. This updated review will allow novices and established researchers to advance apple and Malus biotechnology and breeding programs.

In vitro thermotherapy-based methods for plant virus eradication

Production of virus-free plants is necessary to control viral diseases, import novel cultivars from other countries, exchange breeding materials between countries or regions and preserve plant germplasm. In vitro techniques represent the most successful approaches for virus eradication. In vitro thermotherapy-based methods, including combining thermotherapy with shoot tip culture, chemotherapy, micrografting or shoot tip cryotherapy, have been successfully established for efficient eradication of various viruses from almost all of the most economically important crops. The present study reviewed recent advances in in vitro thermotherapy-based methods for virus eradication since the twenty-first century. Mechanisms as to why thermotherapy-based methods could efficiently eradicate viruses were discussed. Finally, future prospects were proposed to direct further studies.

Cytotoxic, Genotoxic, and Polymorphism Effects on Vanilla planifolia Jacks ex Andrews after Long-Term Exposure to Argovit® Silver Nanoparticles

Worldwide demands of Vanilla planifolia lead to finding new options to produce large-scale and contaminant-free crops. Particularly, the Mexican Government has classified Vanilla planifolia at risk and it subject to protection programs since wild species are in danger of extinction and no more than 30 clones have been found. Nanotechnology could help to solve both demands and genetic variability, but toxicological concerns must be solved. In this work, we present the first study of the cytotoxic and genotoxic effects promoted by AgNPs in Vanilla planifolia plantlets after a very long exposure time of six weeks. Our results show that Vanilla planifolia plantlets growth with doses of 25 and 50 mg/L is favored with a small decrease in the mitotic index. A dose-dependency in the frequency of cells with chromosomal aberrations and micronuclei was found. However, genotoxic effects could be considered as minimum due to with the highest concentration employed (200 mg/L), the total percentage of chromatic aberrations is lower than 5% with only three micronuclei in 3000 cells, despite the long-time exposure to AgNP. Therefore, 25 and 50 mg/L (1.5 and 3 mg/L of metallic silver) were identified as safe concentrations for Vanilla planifolia growth on in vitro conditions. Exposure of plantlets to AgNPs increase the polymorphism registered by inter-simple sequence repeat method (ISSR), which could be useful to promote the genetic variability of this species.

Targeted Metabolic Profiling Indicates Apple Rootstock Genotype-Specific Differences in Primary and Secondary Metabolite Production and Validate Quantitative Contribution From Vegetative Growth

Previous reports regarding rhizodeposits from apple roots are limited, and complicated by microbes, which readily colonize root systems and contribute to modify rhizodeposit metabolite composition. This study delineates methods for collection of apple rhizodeposits under axenic conditions, indicates rootstock genotype-specific differences and validates the contributions of vegetative activity to rhizodeposit quantity. Primary and phenolic rhizodeposit metabolites collected from two apple rootstock genotypes, G935 and M26, were delineated 2 months after root initiation by utilizing gas chromatography/liquid chromatography-mass spectrometry (GC/LC-MS), respectively. Twenty-one identified phenolic compounds and 29 sugars, organic acids, and amino acids, as well as compounds tentatively identified as triterpenoids were present in the rhizodeposits. When adjusted for whole plant mass, hexose, erythrose, galactose, phloridzin, kaempferol-3-glucoside, as well as glycerol, and glyceric acid differed between the genotypes. Phloridzin, phloretin, epicatechin, 4-hydroxybenzoic acid, and chlorogenic acid were among the phenolic compounds found in higher relative concentration in rhizodeposits, as assessed by LC-MS. Among primary metabolites assessed by GC-MS, amino acids, organic acids, and sugar alcohols found in relatively higher concentration in the rhizodeposits included L-asparagine, L-cysteine, malic acid, succinic acid, and sorbitol. In addition, putative ursane triterprenoids, identified based on accurate mass comparison to previously reported triterpenoids from apple peel, were present in rhizodeposits in high abundance relative to phenolic compounds assessed via the same extraction/instrumental method. Validation of metabolite production to tree vegetative activity was conducted using a separate set of micropropagated trees (genotype MM106) which were treated with a toxic volatile compound (butyrolactone) to inhibit activity/kill leaves and vegetative growth. This treatment resulted in a reduction of total collected rhizodeposits relative to an untreated control, indicating active vegetative growth contributes to rhizodeposit metabolites. Culture-based assays indicated an absence of bacterial or fungal endophytes in roots of micropropagated G935 and M26 plants. However, the use of fungi-specific primers in qPCR indicated the presence of fungal DNA in 30% of the samples, thus the contribution of endophytes to rhizodeposits cannot be fully eliminated. This study provides fundamental information for continued research and application of rhizosphere ecology driven by apple rootstock genotype specific rhizodeposition.

Combining Thermotherapy with Cryotherapy for Efficient Eradication of Apple stem grooving virus from Infected In-vitro-cultured Apple Shoots

Apple stem grooving virus (ASGV), a difficult-to-eradicate virus from apple propagative materials, causes serious damage to apple production. The use of virus-free plants has been and is an effective strategy for control of plant viral diseases. This study aimed to eradicate ASGV from virus-infected in-vitro-cultured shoots of four apple cultivars and one rootstock by combining thermotherapy with cryotherapy. In vitro stock shoots infected with ASGV were thermo-treated using an alternating temperature of 36°C (day) and 32°C (night). Shoot tips were excised from the treated stock shoots and subjected to cryotherapy. Results showed that, although thermotherapy did not influence shoot survival rates, it reduced shoot growth and proliferation of in vitro shoots. Shoot regrowth rates decreased while virus eradication frequencies increased in cryo-treated shoot tips as time durations of thermotherapy increased from 0 to 6 weeks. Shoot regrowth and frequency of virus eradication were positively and negatively correlated, respectively, with the size of shoot tips. The protocol established here yielded shoot regrowth rates and virus eradication frequencies of 33 to 76% and 30 to 100%, respectively, in the four apple cultivars and one rootstock. Thermotherapy altered virus distribution patterns, subsequently resulting in production of a larger virus-free area in the thermo-treated shoot tips. Many cells in the top layers of apical dome and some cells in the youngest leaf primordia survived in cryo-treated shoot tips; these cells were most likely free of virus infection. Thus, plants regenerated from the procedure of combining thermotherapy with cryotherapy were free of ASGV, as judged by reverse-transcription polymerase chain reaction. To the best of our knowledge, this is the widest-spectrum technique reported thus far for the production of ASGV-free plants and provides a novel biotechnology for the production of virus-free plants in Malus spp.

Modeling and Optimizing a New Culture Medium for In Vitro Rooting of G×N15 Prunus Rootstock using Artificial Neural Network-Genetic Algorithm

The main aim of the present investigation is modeling and optimization of a new culture medium for in vitro rooting of G×N15 rootstock using an artificial neural network-genetic algorithm (ANN-GA). Six experiments for assessing different media culture, various concentrations of Indole - 3- butyric acid, different concentrations of Thiamine and Fe-EDDHA were designed. The effects of five ionic macronutrients (NH4+, NO3-, Ca2+, K+ and Cl-) on five growth parameters [root number (RN), root length (RL), root percentage (R%), fresh (FW) and dry weight (DW)] were evaluated using the ANN-GA method. The R2 correlation values of 0.88, 0.88, 0.98, 0.94 and 0.87 between observed and predicted values were acquired for all five growth parameters, respectively. The ANN-GA results indicated that among the input variables, K+ (7.6) and NH4+ (4.4), K+ (7.7) and Ca2+ (2.8), K+ (36.7) and NH4+ (4.3), K+ (14.7) and NH4+ (4.4) and K+ (7.6) and NH4+ (4.3) had the highest values of variable sensitivity ratio (VSR) in the data set, for RN, RL, R%, FW and DW, respectively. ANN-GA optimized LS medium for G×N15 rooting contained optimized amounts of 1 mg L-1 IBA, 100, 150, or 200 mg L-1 Fe-EDDHA and 1.6 mg L-1 Thiamine. The efficiency of the optimized culture media was compared to other standard media for Prunus rooting and the results indicated that the optimized medium is more efficient than the others.

Gas exchange measurement as a non-destructive viability assay for frozen-thawed, winter-dormant apple buds

Low temperature studies with winter-dormant buds are severely limited by the lack of a rapid,non-destructive assay for their viability. Investigations involving the winter harvest of ecodormant buds of woody subjects, including cryopreservation, are restricted if viability cannot be assessed until dormancy is broken. If post-treatment grafting indicates low survival of the harvested population then further collection and study has to be delayed until the next winter season. This study trials the use of a portable gas exchange system able to discriminate between live and dead buds rapidly, with the assay confirmed as non-destructive by subsequent micropropagation. Active respiration was recorded for 85% of a winter-dormant Malus domestica buds population that showed 91% viability when grafted (n = 45). Lethally stressed material gave no false positive results. When micropropagated after respiratory measurement, a population viability of 76% was recorded. There was a significant, positive correlation between respiration and fresh weight for buds of mass >10 mg, from a population with a mean fresh weight of 17 mg.

Cryobiotechnology of apple (Malus spp.): development, progress and future prospects

Cryopreservation provides valuable genes for further breeding of elite cultivars, and cryotherapy improves the production of virus-free plants in Malus spp., thus assisting the sustainable development of the apple industry. Apple (Malus spp.) is one of the most economically important temperate fruit crops. Wild Malus genetic resources and existing cultivars provide valuable genes for breeding new elite cultivars and rootstocks through traditional and biotechnological breeding programs. These valuable genes include those resistant to abiotic factors such as drought and salinity, and to biotic factors such as fungi, bacteria and aphids. Over the last three decades, great progress has been made in apple cryobiology, making Malus one of the most extensively studied plant genera with respect to cryopreservation. Explants such as pollen, seeds, in vivo dormant buds, and in vitro shoot tips have all been successfully cryopreserved, and large Malus cryobanks have been established. Cryotherapy has been used for virus eradication, to obtain virus-free apple plants. Cryopreservation provided valuable genes for further breeding of elite cultivars, and cryotherapy improved the production of virus-free plants in Malus spp., thus assisting the sustainable development of the apple industry. This review provides updated and comprehensive information on the development and progress of apple cryopreservation and cryotherapy. Future research will reveal new applications and uses for apple cryopreservation and cryotherapy.

Cryotherapy by encapsulation-dehydration is effective for in vitro eradication of latent viruses from 'Marubakaido' apple rootstock

Apple stem pitting virus (ASPV), Apple chlorotic leaf spot virus (ACLSV) and Apple stem grooving virus (ASGV) are several major viral pathogens of apple trees, responsible for substantial damage to the world's apple industry. This study aimed to evaluate the effectiveness of the encapsulation-dehydration cryopreservation technique to eradicate these viral pathogens from in vitro shoot tips excised from 'Marubakaido' apple rootstock cultures. Axillary shoot tips were excised from in vitro cultures, encapsulated in alginate beads, precultured in MS salts, dehydrated in a laminar flow hood, immersed in liquid nitrogen, then warmed and recovered on medium. After LN exposure, in vitro rooting and acclimatization, recovered 'Marubakaido' plants exhibited 52% survival and 35% regrowth without callus formation. After 8 months of regrowth, PCR analyses revealed that all the plants were free of ACLSV and ASPV, but 2 out of 20 recovered plants were still infected with ASGV. This is the first report in Brazil of the application of cryotherapy to eradicate viral complexes in Malus. Cryotherapy can facilitate the production of virus-free plants by producing high quality plant material.

Cryotherapy: A Novel Method for Virus Eradication in Economically Important Plant Species

Virus diseases have been a great threat to production of economically important crops. In practice, the use of virus-free planting material is an effective strategy to control viral diseases. Cryotherapy, developed based on cryopreservation, is a novel plant biotechnology tool for virus eradication. Comparing to the traditional meristem culture for virus elimination, cryotherapy resulted in high efficiency of pathogen eradication. In general, cryotherapy includes seven major steps: (1) introduction of infected plant materials into in vitro cultures, (2) shoot tip excision, (3) tolerance induction of explants to dehydration and subsequent freezing in liquid nitrogen (LN), (4) a short-time treatment of explants in LN, (5) warming and post-culture for regeneration, (6) re-establishment of regenerated plants in greenhouse conditions, and (7) virus indexing.

Mathematical Modeling and Optimizing of in Vitro Hormonal Combination for G × N15 Vegetative Rootstock Proliferation Using Artificial Neural Network-Genetic Algorithm (ANN-GA)

The efficiency of a hybrid systems method which combined artificial neural networks (ANNs) as a modeling tool and genetic algorithms (GAs) as an optimizing method for input variables used in ANN modeling was assessed. Hence, as a new technique, it was applied for the prediction and optimization of the plant hormones concentrations and combinations for in vitro proliferation of Garnem (G × N15) rootstock as a case study. Optimizing hormones combination was surveyed by modeling the effects of various concentrations of cytokinin-auxin, i.e., BAP, KIN, TDZ, IBA, and NAA combinations (inputs) on four growth parameters (outputs), i.e., micro-shoots number per explant, length of micro-shoots, developed callus weight (CW) and the quality index (QI) of plantlets. Calculation of statistical values such as R2 (coefficient of determination) related to the accuracy of ANN-GA models showed a considerably higher prediction accuracy for ANN models, i.e., micro-shoots number: R2 = 0.81, length of micro-shoots: R2 = 0.87, CW: R2 = 0.88, QI: R2 = 0.87. According to the results, among the input variables, BAP (19.3), KIN (9.64), and IBA (2.63) showed the highest values of variable sensitivity ratio for proliferation rate. The GA showed that media containing 1.02 mg/l BAP in combination with 0.098 mg/l IBA could lead to the optimal proliferation rate (10.53) for G × N15 rootstock. Another objective of the present study was to compare the performance of predicted and optimized cytokinin-auxin combination with the best optimized obtained concentrations of our other experiments. Considering three growth parameters (length of micro-shoots, micro-shoots number, and proliferation rate), the last treatment was found to be superior to the rest of treatments for G × N15 rootstock in vitro multiplication. Very little difference between the ANN predicted and experimental data confirmed high capability of ANN-GA method in predicting new optimized protocols for plant in vitro propagation.

Cryopreservation of banana's cv Grand Naine in vitro rhizomes

The preservation of banana genetic material is usually performed through seedlings. However, most banana cultivars do not produce seed and are propagated vegetatively. Therefore, cryopreservation is a feasible technique that allows the preservation of banana genotypes indefinitely. For the success of cryopreservation protocols, the selection of cryoprotectants and pre-freezing techniques are important factor. Therefore, the objective of this study was to verify the effects of different cryoprotectants with and without 1% phloroglucinol and pre-cooling periods on the development of a protocol for cryopreservation of in vitro rhizomes ofMusa accuminata(AAA) cv Grand Naine banana. The addition of 1% phloroglucinol to the cryoprotective solutions, such as PVS2 enhanced recovery of cryopreserved banana rhizomes. In addition, pre-cooling of explants in ice for 3 hours in PVS2 + 1% of phloroglucinol allowed efficient cryopreservation of banana rhizomes, followed by successful recovery and regeneration of in vitro shoots of banana cv Grand Naine.

Plant Regeneration from Somatic Embryogenic Suspension Cultures of Date Palm

Somatic embryogenesis is one of the most important technologies for plant regeneration of elite date palm cultivars. Recently, considerable progress has been made in the development and optimization of this technique from embryogenic cell suspension cultures. This chapter describes a procedure for the rapid development of a large number of somatic embryos from embryogenic cell suspension cultures. An efficient plant regeneration protocol via somatic embryogenesis from cell suspension cultures starting with shoot-tip explants to plantlet acclimatization also is fully described. Low concentrations of 6-benzylaminopurine (BAP) to 0.3 mg/L and high rate of subcultures each 7 days lead to improve the establishment and multiplication of somatic embryos in suspension cultures by limiting oxidative browning, associated with high total phenols and peroxidase activities. The detailed morphological observations have revealed the cells destined to become somatic embryos. Activated charcoal (AC) at 0.15 g/L has a positive effect on growth rate of somatic embryos by reducing tissue and medium browning, phenolics, and peroxidase activity.

Comparative analysis of bioactive N-alkylamides produced by tissue culture raised versus field plantlets of Spilanthes ciliata using LC-Q-TOF (HRMS)

Spilanthes ciliata (S. ciliata) is a perennial herb of global importance owing to its luscious source of bioactive fatty acid derived amides known as N-alkylamides. It finds application in skin creams, mouth gels and toothpastes. Despite multifaceted applications, a major limitation associated for its commercial application is the scarcity of contamination free plant source, fluctuations in active metabolites due to variation in extraction procedures, and lack of rapid qualitative method for alkylamide profiling. In the current work, attempts were made to 1) optimize conditions for mass propagation of contamination free plants of S. ciliata by tissue culture using leaf discs as explants, 2) establish an optimum extraction ratio of plant/solvent (w/v) for maximum elution of alkylamides and 3) develop a rapid method for qualitative estimation of alkylamide from in vitro raised plants in comparison with that of the field grown counterpart by using LC-Q-TOF (HRMS). To the best of our knowledge, this is the first qualitative report on alkylamide profile of micropropagated whole plant of Spilanthes. The correlation pattern reported in this study may form the basis for using tissue culture raised plantlets of S. ciliata as potential source of bioactive alkylamides on industrial scale.

Estandarización del protocolo de desinfección para la micropropagación de Aspidosperma polyneuron

<p><strong>Título en ingles</strong>: Standardization of the disinfection protocol for the micropropagation of <em>Aspidosperma polyneuron</em></p><p><em>Aspidosperma polyneuron</em> es un especie nativa de la región neotropical, en países como Colombia, Venezuela, Perú, Brasil, Argentina y Paraguay, propio de bosques semideciduos, catalogada desde 1998 por la UICN como “En Peligro (EN)”, debido a que sus poblaciones naturales fueron sometidas a una intensa explotación con fines madereros y su hábitat se vio seriamente degradado por actividades agrícolas y silvopastoriles. Las dificultades para su regeneración natural y el enraizamiento de las estacas, hace que el cultivo <em>in vitro</em> sea una eficaz herramienta para contrarrestar las dificultades reproductivas que presenta. Sin embargo, la presencia de contaminantes que afectan la viabilidad de los explantes, precisa el desarrollo de protocolos que permitan el establecimiento <em>in vitro</em> de la especie. El objetivo de la presente investigación fue lograr el establecimiento aséptico y la inducción de la callogénesis en explantes de <em>A. polyneuron</em>, mediante la evaluación de diferentes tratamientos de desinfección. Los explantes se obtuvieron de individuos de regeneración natural, en el municipio de Armero, departamento del Tolima, los cuales se sumergieron en agua destilada con una gota de Tween® 80 por cada 100 ml, durante 10 minutos y lavados con agua destilada estéril. Se utilizaron como agentes desinfectantes, el hipoclorito de sodio y el dicloruro de mercurio a distintas concentraciones y tiempos de inmersión. De los explantes utilizados: ápices, segmentos nodales y láminas foliares, este último fue seleccionado por su capacidad de producir callos friables de color verde, para lo cual una desinfección con dicloruro de mercurio (HgCl2) al 0.125% durante 10 minutos fue suficiente para el control de la contaminación y bajos índices de oxidación.</p>

Insights into the multifaceted application of microscopic techniques in plant tissue culture systems

Microscopic techniques remain an integral tool which has allowed for the better understanding and manipulation of in vitro plant culture systems. The recent advancements will inevitably help to unlock the long-standing mysteries of fundamental biological mechanisms of plant cells. Beyond the classical applications in micropropagation aimed at the conservation of endangered and elite commercial genotypes, plant cell, tissue and organ cultures have become a platform for elucidating a myriad of fundamental physiological and developmental processes. In conjunction with microscopic techniques, in vitro culture technology has been at the centre of important breakthroughs in plant growth and development. Applications of microscopy and plant tissue culture have included elucidation of growth and development processes, detection of in vitro-induced physiological disorders as well as subcellular localization using fluorescent protein probes. Light and electron microscopy have been widely used in confirming the bipolarity of somatic embryos during somatic embryogenesis. The technique highlights basic anatomical, structural and histological evidence for in vitro-induced physiological disorders during plant growth and development. In this review, we discuss some significant biological insights in plant growth and development, breakthroughs and limitations of various microscopic applications and the exciting possibilities offered by emergent in vivo live imaging and fluorescent protein engineering technologies.

Cytokinin-induced changes in the chlorophyll content and fluorescence of in vitro apple leaves

Cytokinins (CKs) are one of the main regulators of in vitro growth and development and might affect the developmental state and function of the photosynthetic apparatus of in vitro shoots. Effects of different cytokinin regimes including different types of aromatic cytokinins, such as benzyl-adenine, benzyl-adenine riboside and 3-hydroxy-benzyladenine alone or in combination were studied on the capacity of the photosynthetic apparatus and the pigment content of in vitro apple leaves after 3 weeks of culture. We found that the type of cytokinins affected both chlorophyll a and b contents and its ratio. Chlorophyll content of in vitro apple leaves was the highest when benzyl-adenine was applied as a single source of cytokinin in the medium (1846-2176 μg/1g fresh weight (FW) of the leaf). Increasing the concentration of benzyl-adenine riboside significantly decreased the chlorophyll content of the leaves (from 1923 to 1183 μg/1g FW). The highest chl a/chl b ratio was detected after application of meta-topolin (TOP) at concentrations of 2.0 and 6.0 μM (2.706 and 2.804). Chlorophyll fluorescence was measured both in dark-adapted (Fv/Fm test) and in light-adapted leaf samples (Yield test; Y(II)). The maximum quantum yield and efficiency of leaves depended on the cytokinin source of the medium varied between 0.683 and 0.861 (Fv/Fm) indicating a well-developed and functional photosynthetic apparatus. Our results indicate that the type and concentration of aromatic cytokinins applied in the medium affect the chlorophyll content of the leaves in in vitro apple shoots. Performance of the photosynthetic apparatus measured by chlorophyll fluorescence in the leaves was also modified by the cytokinin supply. This is the first ever study on the relationship between the cytokinin supply and the functionability of photosystem II in plant tissue culture and our findings might help to increase plantlet survival after transfer to ex vitro conditions.

Rooting and acclimatization of micropropagated marubakaido apple rootstock using Adesmia latifolia rhizobia

In vitro rooting and the acclimatization of micropropagated rootstocks of apple trees is essential for plant development in the field. The aim of this work was to assess the use of rhizobia of Adesmia latifolia to promote rooting and acclimatization in micropropagated Marubakaido apple rootstock. An experiment involving in vitro rooting and acclimatization was performed with four strains of rhizobium and two controls, one with and the other without the addition of synthetic indoleacetic acid. The inoculated treatments involved the use of sterile inoculum and inoculum containing live rhizobia. The most significant effects on the rooting rate, primary-root length, number of roots, root length, fresh-shoot biomass, and fresh-root biomass were obtained by inoculation with strain EEL16010B and with synthetic indole acetic acid. However, there was no difference in the growth of apple explants in the acclimatization experiments. Strain EEL16010B can be used to induce in vitro rooting of the Marubakaido rootstock and can replace the use of synthetic indoleacetic acid in the rooting of this cultivar.

Gerbera micropropagation

Gerbera jamesonii (gerbera) is an important cut-flower in the global floricultural industry. Micropropagation is the main system used to clonally propagate gerbera in vitro resulting in the production of millions of plantlets each year. Numerous types of explants and protocols for micropropagation have been established and used for gerbera. Shoot tips are the commonly used explant while adventitious shoot induction from the capitulum is also a popular method. Most papers in the literature have focused on testing the influence of different types and combinations of plant growth regulators with the aim of improving the regeneration and multiplication stage of one or few cultivars. Genotype is one of the most influential factors on the response of gerbera in vitro. Despite this, no successful universal protocol has yet been developed for multiple cultivars, limiting the usefulness of current protocols for commercial biotechnology labs. Slow-growing endogenous bacteria are one of the most important problems in gerbera micropropagation but require more studies on control and prevention. Individual shoots are normally easy to root, usually in excess of 90% of plantlets, but the acclimatization stage requires improvements and new technologies to increase the survival of plants. Epigenetic variations in micropropagated gerbera are frequently observed only with high concentrations of cytokinins in the culture medium but somaclonal variation is rare.

Thidiazuron- and Zeatin-induced High-frequency Shoot Regeneration from Leaf and Shoot-tip Explants of Strawberry

Strawberry (Fragaria ×ananassa cv. Camarosa) was evaluated to determine a high-frequency shoot regeneration response for leaf and shoot-tip explants. For direct organogenesis from strawberry leaves, combinations of moderate concentrations of thidiazuron [TDZ (0, 2, and 4 μm)] and 6-benzylaminopurine [BAP (0, 4, and 9 μm)] added into medium containing Murashige and Skoog (MS) basal salts were compared. The most shoots regenerated per leaf explant were observed with 4-μm TDZ. Regeneration from shoot tips was evaluated with 0-, 2-, 4-, 8-, and 16-μm zeatin, kinetin, or 6-α,α-dimethylallylamino purine (2ip) tested individually. Optimum shoot proliferation was achieved from shoot-tip explants on medium containing 4-μm zeatin. Rooting was best without cytokinins in the medium; however, adequate rooting was obtained on the 4-μm zeatin treatment as well.

N9-substituted aromatic cytokinins with negligible side effects on root development are an emerging tool for in vitro culturing

Natural cytokinins as well as the majority of their synthetic derivatives show negative effects on root growth and development. Changes in morphology, primarily linked to the inhibition of the cell division in the meristematic zone, are manifested as thickening and shortening of the primary root and impaired lateral root branching. Rational design of cytokinin derivatives can partially overcome these drawbacks and reduce the negative effects. Using our database of cytokinin derivatives, we selected several aromatic cytokinin analogs with modifications at the N9 atom of the adenine moiety. We found that tetrahydropyranyl and tetrahydrofuranyl substitutions at the N9 atom led to enhanced acropetal transport of the modified cytokinin, and both derivatives also showed weak anticytokinin activity. Consequently, changes in the distribution of the active cytokinin pool together with gradual metabolic conversion of the modified cytokinin to its free form prevent root growth inhibition that limits cytokinin utilization in micropropagation techniques.

Antibiotic-resistant bacteria: a challenge for the food industry

Antibiotic-resistant bacteria were first described in the 1940s, but whereas new antibiotics were being discovered at a steady rate, the consequences of this phenomenon were slow to be appreciated. At present, the paucity of new antimicrobials coming into the market has led to the problem of antibiotic resistance fast escalating into a global health crisis. Although the selective pressure exerted by the use of antibiotics (particularly overuse or misuse) has been deemed the major factor in the emergence of bacterial resistance to these antimicrobials, concerns about the role of the food industry have been growing in recent years and have been raised at both national and international levels. The selective pressure exerted by the use of antibiotics (primary production) and biocides (e.g., disinfectants, food and feed preservatives, or decontaminants) is the main driving force behind the selection and spread of antimicrobial resistance throughout the food chain. Genetically modified (GM) crops with antibiotic resistance marker genes, microorganisms added intentionally to the food chain (probiotic or technological) with potentially transferable antimicrobial resistance genes, and food processing technologies used at sub-lethal doses (e.g., alternative non-thermal treatments) are also issues for concern. This paper presents the main trends in antibiotic resistance and antibiotic development in recent decades, as well as their economic and health consequences, current knowledge concerning the generation, dissemination, and mechanisms of antibacterial resistance, progress to date on the possible routes for emergence of resistance throughout the food chain and the role of foods as a vehicle for antibiotic-resistant bacteria. The main approaches to prevention and control of the development, selection, and spread of antibacterial resistance in the food industry are also addressed.

Review: role of carbon sources for in vitro plant growth and development

In vitro plant cells, tissues and organ cultures are not fully autotrophic establishing a need for carbohydrates in culture media to maintain the osmotic potential, as well as to serve as energy and carbon sources for developmental processes including shoot proliferation, root induction as well as emission, embryogenesis and organogenesis, which are highly energy demanding developmental processes in plant biology. A variety of carbon sources (both reducing and non-reducing) are used in culture media depending upon genotypes and specific stages of growth. However, sucrose is most widely used as a major transport-sugar in the phloem sap of many plants. In micropropagation systems, morphogenetic potential of plant tissues can greatly be manipulated by varying type and concentration of carbon sources. The present article reviews the past and current findings on carbon sources and their sustainable utilization for in vitro plant tissue culture to achieve better growth rate and development.

Biotechnological methods of in vitro propagation in willows (Salix spp.)

Many populations of high-mountainous relic dioecious willows in Central Europe only consist of female individuals and are thus limited in their reproductive potential. We completed micropropagation experiments with shoot apexes and nodal segments of common and endangered willow (Salix) species, which can help to reintroduce autochthonous genotypes to their natural sites. Until recently, cultivation of green young shoot apexes of S. alba and S. lapponum showed the highest percentage of regeneration. We successfully applied the two-times-sterilisation due to high contamination of natural explants. The OK medium was the most efficient culture medium. In vitro propagation of willows with unisexual catkins, anther and ovule cultures were tested and optimised. Isolated anthers were cultivated on selected media and then microcallus and calluses of S. caprea and calluses of S. viminalis were formed on the A medium. Among various tested and optimised media for the ovule culture, the CP medium was the most efficient one. In this case, only the microcalluses of S. viminalis were observed. We developed biotechnological procedures that can be useful in conserving fragmented populations of high-mountainous willows.

In vitro culture of lavenders (Lavandula spp.) and the production of secondary metabolites

Lavenders (Lavandula spp., Lamiaceae) are aromatic ornamental plants that are used widely in the food, perfume and pharmaceutical industries. The large-scale production of lavenders requires efficient in vitro propagation techniques to avoid the overexploitation of natural populations and to allow the application of biotechnology-based approaches for plant improvement and the production of valuable secondary metabolites. In this review we discuss micropropagation methods that have been developed in several lavender species, mainly based on meristem proliferation and organogenesis. Specific requirements during stages of micropropagation (establishment, shoot multiplication, root induction and acclimatization) and requisites for plant regeneration trough organogenesis, as an important step for the implementation of plant improvement programs, were revised. We also discuss different methods for the in vitro production of valuable secondary metabolites, focusing on the prospects for highly scalable cultures to meet the market demand for lavender-derived products.